We shall describe such binoculars.
They comprise, in a conventional manner, an observation channel which comprises an image sensor and a laser telemetry channel termed the laser channel; they also comprise a display screen common to the two channels on which the image arising from the image sensor appears and on which are positioned a firing reticle demarcating the sighting axis of the laser telemeter and a reticle demarcating the center of the image sensor. These reticles generally have the form of a cross. The laser beam of the telemeter is emitted in a very narrow sector typically of about 1 mrad, thus dictating very precise aiming of the laser. Harmonization, that is to say alignment of the axes between the laser channel and the observation channel, is performed in the factory. To telemeter the target, the operator points the binoculars so as to position the laser reticle on the target and then the shot is fired by pressing a push-button.
It is known practice to equip such binoculars with a device for stabilizing the image which makes it possible to compensate for the perturbing movements of the operator who is holding the binoculars in his hands. This stabilization makes it possible to keep the sighting axis of the observation channel constant in spite of small movements of the binoculars; these perturbing movements of the operator are limited to low frequencies with a high cutoff frequency of about 2 Hz. But the stabilization must not prevent tracking of the operator's movements that are not stabilization offsets but deliberate displacements of the binoculars by the operator such as a panoramic displacement movement when for example searching for a zone of interest. For this purpose the image is recentered continuously at very low frequency. Indeed, the erratic movements of the observer correspond to displacements of the binoculars of low amplitudes and of high temporal frequencies whereas deliberate movements correspond to displacements of large amplitudes and of low frequencies.
Through this stabilization, a stable image is therefore obtained but, as a consequence, the laser axis in this image shifts, and it is humanly difficult to aim at the target without moving for a long enough time to perform the telemetry firing; the previous firing procedure no longer works.
One solution consists in suppressing the stabilization during the telemetry phase.
Another solution consists in stabilizing the binoculars themselves as on bulkier equipment such as stabilized optronic turrets; such equipment uses mechanical devices which stabilize both the axis of the imaging channel and that of the channel of the laser telemeter.